PV inverter up/downsizing

EVandPV

Our pv was installed in 2012 and at the time, the thinking was that downsizing the inverter below the output of your solar array was the way to go.
8 years on, is this still the case or have inverters evolved to the point where upsizing or matching the panel ouput is preferable ?

joefizz

Effectively it has always been about matching the inverter to the panel output.

Just not rated output but actual output.
When my panels were installed the actual rules were based on a maximum number of panels (14) using 250w panels as a guideline so coming in under 3.6kw. Of course here in NI they will never achieve that and with losses and effective headroom I probably could have gotten away with a 3kw inverter instead of 4kw but as I installed 14 275w panels it was wise to give that extra bit of leeway, and they never topped out either.
I could probably install 6-6.5kw of panels here in my orientations and with engineering headroom on the 4kw solaredge probably only top out less than 5 days per year, weather dependent and over a couple of years panel degradation would take care of that. Obviously 300 miles south it would be completely different matter...

EVandPV

joefizz said:

Effectively it has always been about matching the inverter to the panel output.

Just not rated output but actual output.
When my panels were installed the actual rules were based on a maximum number of panels (14) using 250w panels as a guideline so coming in under 3.6kw. Of course here in NI they will never achieve that and with losses and effective headroom I probably could have gotten away with a 3kw inverter instead of 4kw but as I installed 14 275w panels it was wise to give that extra bit of leeway, and they never topped out either.
I could probably install 6-6.5kw of panels here in my orientations and with engineering headroom on the 4kw solaredge probably only top out less than 5 days per year, weather dependent and over a couple of years panel degradation would take care of that. Obviously 300 miles south it would be completely different matter...

EVandPV

Cheers Joe.

Probably not worth considering an upgrade here then.

Pile_o_stone

It would impact your FiT payments if you increased the size of your array. Annoyingly they decided to base payments on the output of the solar array rather than the output of the inverter.

pinnks

I am also not sure why you would upgrade an inverter as you are highly unlikely to recoup the investment.  When it breaks, fix it but otherwise just leave it to its job, irrespective of whether you could theoretically get a couple of extra kWh out of a different inverter.
I once considered upgrading my system to better cope with my shading issues (SolarEdge was quite embryonic and/or not understood by most installers when I was looking around).  If I did, I might get an extra 3kWh per day for, say 180 days, making an extra 540kWh or so per year.  With my FiT of approx. 20p per kWh, that would equate to about £100 per year but cost me well over £1,000 to achieve. Annoying as it may be to see that chimney shadow creep across the panels every day, it doesn't make economic or any other type of sense to solve it.  When the inverter dies I might consider doing something.

Ectophile

Also bear in mind that solar panels do gradually deteriorate over the years.  The assumed life is about 25 years.  So an inverter matched to the output of the panels when new may never generate at the maximum expected.

Solarchaser

Yeah the thinking is still the same.
Oversize panels/undersize inverter.
Popular to double size in Aus apparently.
Last year i bought a growatt 3600 which took a max of 6600w of panels, so i fitted 6600w of panels to my garage roof.
If the inverter wasnt a pile of junk it would probably have worked really well.

I have the *standard* 4kw of panels (16x 250w) with a 3600w inverter, and it hits the 3600w pretty often, it did it for a short tine today actually.

Martyn1981

I assume the thinking remains the same, as panels rarely maintain close to their full rating, perhaps just seconds in the summer, but minutes in April/October if the temp is very low. Also for the UK, the inverters don't work too hard (close to max) for much of the year, nor process as much leccy as ones in sunnier countries that may see 40-80% more annual gen.

I'm thinking back nearly 10yrs, but I recall SMA doing some side by side testing, the 3600TL beat out the 4000TL on a 4kWp system, and I think the winner on a 5kWp system was a 3800TL, can't remember who came second/third out of the 3600 and 4000.

Trying to think of a counter argument, and I suppose that might be that a larger inverter would last longer (not worked as hard), but time seems to be teaching us that inverters are lasting longer than expected, and as mentioned, aren't stressed as much in the UK.

Totally agree about panel degradation, which is also smaller than expected, perhaps 0.4%pa, v's early guesses closer to 2%, but it still counts. And I did upgrade my ESE system to Solaredge due to a lot of small shading issues, but economically I wouldn't recommend unless there are other factors - in my case access via a Velux and safety harness kept costs to a minimum, and I wanted to open up the system to a possible expansion in the future (getting closer, fingers crossed). The last two years have given me my 1st and 3rd best years, and 5% higher than pre Solaredge average, but weather could be a major factor, so hard to guess at the benefits yet.

joefizz

EVandPV said:

Cheers Joe.

Probably not worth considering an upgrade here then.

FWIW as others have said, probably not. Its worth looking up the specs of your inverter to see what it is capable of dealing with. Most have larger headroom or temporary capacity built in. Its then a matter of seeing how your whole individual system performs and seeing is it worth changing/adding panels depending on your current agreements etc. There might be allowance for replacing panels that have 'malfunctioned' if you get what I mean. Would be hard to get replacement 250w panels now 300w would be more 'standard' and someone in another thread has installed the panels that are transparent so might be worth looking at those in the future.

Again FWIW I saw the inverter as an install once, run until it dies, fix then run again piece of equipment. Im probably giving mine the kiss of death but they arent particularly complex bits of kit (I have the solaredge one with all matched mini inverters so probably overcomplicated) so other than heat damage, heating effect and capacitors blowing they should last a reasonably long time.

Above all else consider maintenance and by that I mean visual inspection in the loft/wherever and checking the panels and occasionally giving them a good clean. Its more likely things like wires rubbing on metal due to wind/rain/snow and birds etc will cause more damage in the long run. I bought a cheap small video drone once for checking the state of the chimney bricks (cheaper than getting someone out to inspect) and use it once or twice a year to give the panels a fly past.

In the 2 years they have been installed Ive went up to have a look once and ended up cable tying a couple of the wires around the solaredge mini inverters just to be sure to be sure.
Along with connectors, wiring etc the inverter would be last on my list to change/upgrade and it would only be if I couldnt repair it but YMMV.

EVandPV

Thanks guys.
Definitely not looking to add more panels as there's no more room on our roof.
Was just curious to see if inverter tech had moved on in the 8 years our system has been running and if it was possible to squeeze a few more kwh out of it.
It's all still working as well as it did on day one as far as I can see so will leave as is.